My DD(17)'s knee swelled 24 hours after a gymnastics event. She didn't remember injuring it. This was 2 months ago. Ever since then, she can't fully bend the knee, so she can't sit back on her heels etc without pain (she says the pain is "inside").
No pain at any other times, and can still play sport if doesn't involve deep knee bends. She says it is stiff sometimes bending it if her legs have been out straight for a while.
Any ideas?